1. Technical Field
The present invention relates to a method of manufacturing a circuit board, a method of manufacturing a semiconductor device, and a method of manufacturing an electro-optical device including a liquid crystal device, an organic electroluminescent (EL) device, or an electrophoretic device, and in particular to a method of forming a passage in an insulation layer (contact hole forming method).
2. Related Art
Semiconductor devices using organic transistors made of a semiconductor material, an organic insulation material, an organic conductive material, or the like have been developed. A transistor made of such an organic material (hereinafter, referred to as “organic transistor”) is generally formed by depositing or coating an organic material on a plastic substrate. The combination of an organic material on a plastic substrate has great flexibility, which makes it ideal for the manufacture of electronic devices using organic transistors, which are light, thin, and bendable.
The organic transistor is formed by repeatedly alternately performing a step of depositing (or coating) an organic insulation material or an organic conductive material and a step of patterning the organic insulation material or the organic conductive material. In this method, a contact hole forming process to form a contact hole in an interlayer insulation layer is needed to enable wiring interconnection between conductive layers.
As for a method of forming a contact hole in the organic insulation material, a photolithography process or an etching process is disadvantageous in that it is difficult to strip off photoresist serving as a mask from a base layer made of an organic insulation material because the photoresist is made of an organic material (polymer) and further in that an organic semiconductor material which is an under-layer of the mask deteriorates because the organic semiconductor material causes photoreaction with the mask during exposure.
In order to solve the problem, JP-A-2002-26362 and JP-A-2006-41180 disclose techniques in which a contact hole is formed without using a photolithography process or an etching process. JP-A-2002-26362 discloses a punching method using a heated puncher, in which a contact hole is formed in a stacked structure using the heated puncher. JP-A-2006-41180 discloses a chemical method in which a contact hole is formed by chemically dissolving an inter-layer film 32 by use of a solvent contained in a needle while mechanically penetrating the inter-layer film 32 using the needle.
The above-mentioned techniques have the following disadvantageous effects. First, at the time of pricking the needle in the inter-layer insulation film, it is apt to generate residue with a height of several micrometers around an edge of a contact hole because the inter-layer insulation film made of an organic insulation material (polymer) has ductility and high viscosity. Second, it is difficult to check whether the inter-layer insulation film is completely removed and a base electrode under the inter-layer film is exposed. In particular, such checking is more difficult in the case of using a flexible substrate having low rigidity, such as a plastic substrate. The above problems lead to insecure interconnection (electrical conduction) between conductive layers (electrode•wirings) when the conductive layers are connected by a conductive material provided in the contact hole.